the pedicellariæ of Echinoderms are somewhat similar in appearance, they cannot be supposed to perform a like office in animals so well endowed with locomotive powers, and so voracious in their attacks upon creatures almost as large as themselves, such as oysters and other molluscs. Star-fishes are, indeed, held to be the most destructive enemies of oyster-beds.

We must not conclude our paper without some notice of the Feather-star (Comatula rosacea), perhaps the most interesting of British star-fishes-one which is unique in the gracefulness of its form and the exquisite beauty of its colouring, whose life-history is very remarkable, and which possesses the additional interest of being the only living representative in our seas of the group of organisms so familiar to us in the fossil state as Encrinites. The delicate structure of this species renders it impossible to preserve it satisfactorily in a dry state: it is only when exhibited in some preservative fluid that any idea can be formed of the elegance of the living animal. The central cup-shaped body gives origin to five rays, which divide so near the base as to appear like ten. These are furnished throughout their length with membranous pinnæ or fins, with which the creature swims freely. It is said to propel itself somewhat in the manner of a medusa, using its arms alternately, five of them being in action while the other five are quiescent.

In the year 1823, Mr. J. Vaughan Thompson (whose name will be held in lasting remembrance as the discoverer likewise of the metamorphoses of the Crustacea), found in the Cove of Cork a creature about three-quarters of an inch in height, resembling very much a minute feather-star set upon a flexible, articulated stem. This he described and named Pentacrinus Europaus; but in 1836 he published a second paper in which he announced his discovery that the Pentacrinus was but the young state of Comatula, and this opinion is now held by all zoologists. Mr. Thompson found all his Pentacrini attached to Zoophytes, but they have been taken by others amongst Fuci, though never upon stones or shells. The larger Comatulæ are mostly met with in deep water, being taken by the dredge; and it would appear that they come into the shallower water near shore for the purpose of depositing their ova in the littoral groves of Zoophytes and Laminariæ. The development of the animal from the ovum, through the pentacrinoid stage to the mature form of Comatula, has never, I believe, been watched uninterruptedly: the feather-star has not yet been caught in the very act of leaving its encrinital stem, but for all that, the facts which have been observed, though they rather invite than preclude further investigation, are amply sufficient to place this most interesting episode of animal life beyond the doubt of any but the most inveterate sceptic.

CLUSTERS AND NEBULE. OCCULTATIONS.

BY THE REV. T. W. WEBB, M.A., F.R.A.S.

THE lover of system may perhaps have felt disposed to take exception to the arrangement of our little catalogue of Double Stars, and with some justice, from his point of view. Large and small, close and wide, conspicuous and difficult, were all intermingled in the greatest apparent disorder. This, however, was deliberately done, on the ground of the observer's convenience; the intention not having been to provide a classified catalogue, but a familiar guide to the amateur through each successive month. A similar apology, or, at any rate, explanation, is even more requisite at the commencement of our present list, since the objects we shall enumerate are yet more dissimilar from each other, and will be arranged in a manner still more unlike systematic classification. The difference is extreme between a coarse group of bright stars visible even to the unaided eye, and a faint and almost evanescent haze, whose stellar nature depends upon inference alone, or possibly may be liable to suspicion. The reader, however, will find them all here, arranged merely to suit his convenience: and possibly he may not be displeased with the resulting effect of variety and contrast. It should also be borne in mind that though the comprehensive title "Clusters and Nebula" is more appropriate than either designation would have been separately, it indicates in many cases a distinction without a difference; nearly all clusters that are visible at all with the naked eye appearing to it as nebulæ, and an increasing proportion of telescopic nebulæ being resolved into clusters as we increase the aperture of our instruments. The boundary-line has an actual existence in every telescope, when it ceases to recognize individual points. of light in the haze; but it is different in different instruments, and it has no existence in nature, or at any rate the question of its existence is one of the most perplexing, as well as most interesting, points in modern astronomy, and therefore any arrangement which pre-supposes a definite separation, must needs be, in the present state of our knowledge, merely arbitrary. Our commencement will be a glorious one. We shall take up first an object, the very finest perhaps of its class in our latitudes

I. The Cluster in the Sword-hand of Perseus, in astronomical symbolism 33 H vi., that is to say, No. 33 in Sir W. Herschel's list of "very compressed and rich clusters of stars,' which form the sixth class in his celebrated catalogue. Being obvious to the naked eye as a nebulous spot of some extent, or rather, with 34 H vi., as two contiguous nebula, this will be

immediately found in the galaxy between Cassiopea and the principal stars of Perseus (see INTELLECTUAL OBSERVER, xi. 373). Even small telescopes will here disclose a scene of wonder. Smyth has described it as a brilliant mass of stars, from 7th to 15th mags., filling the whole field of view, and emitting a peculiarly splendid light. In the centre, he says, is "a coronet, or rather ellipse, of small stars, above an 8th mag. one. The 7th mag. star which follows is handsome from the blackness of the space immediately around it. . This is followed by another gorgeous group of stars from the 7th to the 15th mags. at about 3, and nearly on the parallel. It is 34 vi. The components gather most towards the centre, but there is little disposition to form; the sprinkle, however, is in a direction parallel to the equator. One of the central individuals is of a fine ruby colour, and a 7th mag. in the n fis of a pale garnet tint, with two sparkling but minute triplets south of it. These two clusters are quite distinct, though the outliers of each may be brought into the same field under rather high powers; and, on the best nights, the groups and light are truly admirable, affording together one of the most brilliant telescopic objects in the heavens. It is impossible to contemplate them and not infer that there are other laws of aggregation than those which obtain among the more scattered and insulated stars."

If these clusters are, as Sir W. Herschel thought, a protuberant part of the Milky Way, and if magnitude is not a wholly fallacious guide as to distance, the splendour of their components, as compared with the average minuteness of the individuals which make up the feeble light of the galaxy, would indicate that they must be very much nearer to us than the general situation of that zone, and that this region must consequently be the foreshortened projection of a long irregular stream of stars, whose direction is towards the spectator. The whole of this district is truly magnificent. Whoever would gain an extended idea of the infinite riches of the Creator's handiwork, may find it in sweeping over this, as well as many other portions of the galaxy, where He has literally

"Sowed with stars the heaven thick as a field."

Our second object will be one of an entirely different character; less brilliant, indeed, but mysterious in the highest degree:

II. The Great Nebula in Orion. Beneath the lowest, or most easterly of the three gems of Orion's belt, we see a depending line of smaller stars, forming the sword,* one among

In 1807, the University of Leipzig formed a new constellation out of the belt and sword of Orion, to be called by the name of Napoleon. What a melancholy, but instructive, instance of human weakness!

which, having a more hazy aspect than the rest, will be recognized at once as a nebula by the naked eye in a clear night. It is singular, therefore, that it should not have been included among the "nebulosa" of the ancients; and still more singular that Galileo, in making the earliest telescopic delineation of this region of the sky, including the very stars in question, should have missed it; for small as his instrument was, it was abundantly adequate to disclose to him a marvellous appearance in the midst of them. We can only suppose that he may have mistaken it for the effect of moisture upon his eye-glass, but if so, his examination must have been a very cursory one: and this, indeed, we should deduce from the roughness of his sketch, unless, as is so frequently the case, engravers and copyists may have been in fault. The first notice of it which has been found is a correct though incidental description of it by Cysatus shortly after, who compared with it the telescopic aspect of the grand comet of 1618. Huygens, not being aware of this, announced it in 1656 as a discovery, the like of which he had not been able to observe anywhere else among the stars, and sketched it roughly with a power of 100 in his 23 feet refractor. His impression was that no telescopes but his would show it; a curious example of the amount of self-deception which may result from unchallenged success, for we cannot imagine that the object was less visible to the naked eye then than now. He saw, however, as it appears, only three of the stars in the trapezium, which forms so conspicuous a centre-piece; the 4th was added by Picart in 1673.* It was natural that so remarkable an object should attract much notice, and many descriptions and figures by the earlier astronomers are extant; but for want of optical power their results are of little value. Sir W. Herschel figured it in 1774; it was the first object viewed with his 40 feet reflector in 1787; and he gave another design in 1811 Schröter represented it in 1794; Sir J. Herschel in 1824, and again at a greater altitude and in a clearer sky at the Cape of Good Hope in 1837; and among other modern observers, the Earl of Rosse, Lamont, Lassell, Bond, Liapounov, Struve, and Secchi, have directed much attention to it. Notwithstanding the magnificent instrumental means and unquestioned ability brought to bear upon it by these great astronomers, their representations are not altogether accordant, and, generally speaking, they are not fully satisfied with each other's work. There must indeed be always a margin of uncertainty left as to these ill-defined and cloudy patches; and Sir J.

Arago says, by Dominic Cassini; but without reference: and this seems improbable, as Mairan, who gives the exact date of Picart's discovery (March 20), makes no mention of Cassini's. Picart's observation remained, however, in MS. till 1731. Cassini died in 1712.

Herschel has cautioned us that "very great differences will occur in the descriptions of one and the same nebula taken on different nights, and under different atmospheric circumstances, as well as in different states of the mirror and the eye; nor will it at all startle one accustomed to the observation of nebulæ to see such an object described at one time as faint, small, round, and at another as bright, pretty large, pretty much extended, resolvable, etc.;" but after making every allowance on this score, as well as for the great difficulty of representing such an object well, it must be admitted that the variations are more considerable and perplexing than, considering the character of the observers, we might have expected.

Are we then thus forced upon the supposition of actual physical change? Such an idea would be sufficiently astonishing, when the enormous magnitude of so remote an object is considered; but it has been seriously entertained. Herschel I. had been led to suppose it fully established, from the disappearance of a misty envelope round certain stars adjacent to the nebula, and from an alteration in the direction of one of its branches; and though his son had at one time come to the conclusion that there were no differences which would not admit of explanation upon the grounds already mentioned, and that there was no reliable evidence of change, he subsequently felt obliged to alter his opinion, from the dissimilarity between his own designs in England and at the Cape; other discrepancies he could account for, from practice and a superior instrument and climate; but as to one part, he says, "it seems hardly possible to avoid the conclusion of some sensible alteration having taken place. No observer now, I think, looking ever so cursorily at this point of detail, would represent the broken, curved, and unsymmetrical nebula in question . . . as it is represented in the earlier of the two figures; and to suppose it seen as in 1837, and yet drawn as in 1824, would argue more negligence than I can believe myself fairly chargeable with." This would be indeed most weighty testimony, even if it stood alone; but such is by no means the case. In 1852, Lassell, after observing the nebula carefully with his 24-inch speculum, says, "a comparison of Sir J. Herschel's, Mr. Bond's, and my own drawings of this wonderful object must, I think, suggest the idea of change in the nebula, or variability in the stars, or otherwise a less uniformity of delineation of the same things than might have been hoped for." In 1856 W. Struve was led by the observations of Liapounov, who had during four years been most scrupulously measuring and delineating the nebula at Kazan with a 9-inch achromatic, to infer that it may be subject to changes of form and relative brightness in its different